Trends in the electric power utility automation sector, specifically substation automation, have been driving towards common communications architecture. The initiative was begun in the early 1990s driven by the major North American utilities under the technical auspices of Electric Power Research Institute (EPRI). The resulting standard that emerged is known as the Utility Communications Architecture 2.0 (UCA2). At the heart of this architecture is the substation LAN (Local Area Network) based on Ethernet. However, one of the major requirements for electronic devices used in substations as part of a protection and control system is their ability to operate reliably in harsh environmental conditions. Harsh environmental conditions include conditions having both adverse atmospheric conditions and adverse electrical conditions. Substation environments are much harsher than the office environments where the overwhelmingly majority of Ethernet equipment resides and was designed for.
It would therefore be desirable for the Ethernet switch, which forms the backbone of the substation LAN, to be as reliable and robust as other IEDs (Intelligent Electronic Devices) designed specifically to operate in harsh substation environments. One such group of IEDs are protective relays which perform the function of protecting the power system from fault conditions and other anomalies. Modern, microprocessor based protective relays are adhering to the UCA2 standard and providing one or multiple Ethernet ports ready to connect to suitable Ethernet Switches.
However, the prior art Ethernet switches and some other electronic devices do not meet these standards. In order for prior art switches and other electronic devices to be as reliable and robust as the protective relaying IEDs and other electronic devices, they must generally adhere to ANSI/IEEE C37.90 standards (US) and the IEC60255 standard (Europe) which were designed for protective relaying IEDs and other intelligent devices found in electrical substations. In particular, it would be desirable to Ethernet switches to pass the following electrical and atmospheric type tests:
(A) Electrical Environment
                1. Surge Withstand Capability as per ANSI/IEEE C37.90.1 (1989), namely withstanding 2.5 k Voscillatory transients, 4.0 kV fast transients applied directly across each output, input and power supply circuit.        2. Surge Immunity as per IEC 61000-4-5 (1995 Level 4) standards.        3. High Frequency Noise Disturbance as per IEC 60255-22-1 (1988 Class III) standards.        4. Fast Transient Disturbance as per IEC 60255-22-4 (1992 Class IV) standards, namely withstanding 4 kV, 2.5 kHz applied directly to the power supply inputs and 4 kV, 2.5 kHz applied directly to all other inputs.        5. Dielectric Withstand as per ANSI/IEEE C37.90-1989 and IEC 60255-5: 1977 standards.        6. High Voltage Impulse Test as per IEC 60255-5: 1977 standard.        7. Electrostatic Discharge as per IEC 60255-22-2: 1996 Class 4 and Class 3 standards.        8. Radiated Radio Frequency Immunity as per IEEE C37.90.2 and IEC 61000-4-3 standards.(B) Atmospheric Environment        1. Temperature: Cold at −40° C. as per the IEC 60068-2-I standard and dry heat at 85° C. as per IEC 60068-2-2 standard.        2. Temperature Cyclic: −25° C. to +55° C. as per IEC 60255-6 (1998) standard.        3. Relative Humidity: 5 to 95% as per the IEC 60068-2-2 standard.        
Referring now to FIG. 1A, an electronic circuit block diagram, shown generally by reference numeral 10, of a conventional commercial Ethernet Switch is shown. The circuit 10 consists of an Ethernet Media Access Controller (MAC) block I which typically provides a plurality of communications ports each adhering to the Reduced Media Independent Interfaces (RMII) signaling specification as put forth by the version 1.2 of the RMII Consortium. These RMII ports interface to a physical layer device 4, referred to as a PHY, which converts the RMII signals to differential transmit and receive signal pairs in accordance with the IEEE 802.3 10BaseT and or 100BaseTX standards. These signals are then noise filtered by the filter block 5a and electrically isolated via pulse transformers 5b which also couple the signals to the RJ45 style connector receptacles 5c which are typical of commercial grade Ethernet Switches. The RJ45 interface 8 typically accepts TIA/EIA 568 category 5 (CAT-5) unshielded twisted pair copper wire cables. Power is typically provided by a single power supply block 6 and cooling of the electronics is also typically provided by a low-voltage DC powered cooling fan 7 typical of those found in personal computers.
The electronic circuit 10 illustrated in FIG. 1A has numerous shortcomings when used in a harsh environment including a utility substation environment. In particular, the switch is susceptible to electrical transients and electromagnetic interference being coupled into the device via twisted pair copper cables 8. This is extremely undesirable since it could result in corruption of real-time mission critical control messages being transmitted over the network via the switch. Moreover, actual damage to the switch itself is possible if high voltage electrical transients are directly coupled into the device via the copper cables overcoming the limited electrical isolation (typically 1000V to 1500V RMS) provided by isolation transformers 5b. Another point of electrical transient susceptibility in the design of FIG. 1A is the power supply input 6a. The power supply block 6 must be capable of enduring electrical transients at levels of 2 kV to 5 kV as specified by the ANSI/IEEE C37.90 and IEC 60255 standards. This is not a requirement for commercial grade Ethernet Switches and thus the power supply inputs 6a do not provide suitable transient suppression circuitry. Furthermore, commercial grade Ethernet switches are not specifically designed to withstand EMI (Electromagnetic Interference) levels of 35V/m as specified by ANSI/IEEE C37.90.2 (1995) which is typical of many substation environments.
Accordingly, conventional circuit 10 suffers from the disadvantage that it is susceptible to electrical transients and electromagnetic interference at levels which are possible, or even common, in utility substation environment. The design of FIG. 1A is also susceptible to mechanical breakdown because of the use of rotating cooling fan 7 required to cool the electronic components. Thus the reliability of the Ethernet Switch is determined by the reliability of the fan which is the only moving mechanical part in the design and typically has the lowest Mean-Time-Between-Failures (MTBF) value, such as less than 10,000 Hrs, compared to electronic components which have MTBF values of greater than 450,000 Hrs. It would be highly desirable to eliminate the fan block 7 from the design and improve the reliability of the Ethernet Switch to MTBF levels similar to those of the IEDs, which would be connected to it, namely greater than 450,000 Hrs. Furthermore, the typical operating temperature range of commercial Ethernet Switches having the circuit 10 shown in FIG. 1A is 0° C. to 40° C. (ambient) with fan cooling 7. However, the operating temperature range for devices in the substation environment such as protective relays is specified by the IEC 60255-6 (1998) standard as −25° C. to +55° C. Therefore, not only is the circuit 10 of FIG. 1A susceptible to failure, it also does not meet the requirements of the environmental conditions which are possible, or even common, in utility substation environments.
Furthermore, because of the mission critical nature of the application, that being the use of the substation LAN to send real-time control messages during power system fault conditions, the availability or “up time” of the Ethernet Switch is critical to proper operation of the protection and control system. A further point of susceptibility of the design of FIG. 1A is the power supply block 6. If the power supply block 6 fails then the Ethernet Switch fails and is not available to provide the backbone of the LAN during the critical period of time where the protection and control system needs to respond in the order 4 to 100 ms.
One potential communication equipment fault which may arise, particularly in, but not exclusively in electric utility substations, includes a ground potential rise (GPR). While communication equipment in electric utility substations, and other harsh environments, must be capable of withstanding high levels of electromagnetic interference caused by a variety of phenomenon, one particular phenomenon which occurs in such harsh environments occur for instance when a high voltage (for example 500 kV or higher) conductor experiences a ground fault condition, such as being shorted to earth ground. In this type of phenomenon, ground currents will flow that can create high levels of ground potential rise (GPR) within a localized area, such as a switch yard in the case of an electric utility substation, may occur. Because the Ethernet switches and other IEDs may be located in a network that covers a large area, a ground potential rise within one location may have catastrophic effects to the components in that area and/or the components in other areas. For instance, any equipment with copper wire connections across the location of the ground potential rise, such as, for example, an Ethernet switching hub located in the control room connecting to a protective relay device or intelligent switch gear device in a switch yard, will experience high levels of ground potential rise which can damage the equipment by causing the galvanic isolation barriers between the two connected devices, such as the Ethernet switch in the control room and the protective relay in the switch yard, to break down. In this way, the internal components of the electronics could be exposed to high voltages and currents causing potential physical damage. For communication equipment interfacing using electrical connections such as by copper wire, or a combination of electrical connections and fibre optical media, and/or a single electrical connection using copper wire or other conductive material, any ground potential rise presents a serious concern.
FIG. 1B illustrates a ground potential rise in a network 150 comprising a conventional Ethernet switch 102 and end device 120 (which may be an intelligent electrical device or merely an electrical device “which does not have a microprocessor”) in one embodiment of conventional devices 102, 120. As illustrated in FIG. 1B, which, for illustrative purposes only, relates to a substation environment, the Ethernet switch 102 having a connection to ground A is physically located, for instance, by a cable 110 from an end device 120. The end device 120 is connected to ground B, which is a distance of up to 100 m from ground A. In the case of a ground potential rise with respect to either ground A or ground B, such as may occur when a high voltage conductor experiences a ground fault condition, such as being shorted to ground, a ground potential rise could be created at either ground A or ground B. In this situation, electrical transients in the form of a ground potential rise can exceed 5 kV during ground faults in harsh environments, such as substation environments. Equipment, such as Ethernet switch 102 and end device 120 which are connected by an electrically conductive connection, such as cable 110, but separated by a sizeable distance, can experience high potential differences across their respective Ethernet ports 104, 114. These potential differences can exceed the typical rating of isolation 106, 116 for conventional Ethernet ports 104, 114, respectively, which is typically 1200 Volts Root Mean Square (VRMS). In this situation, the galvanic isolation in excess of 4000 VRMS would generally be required in order to prevent physical damage to the Ethernet equipment, such as dielectric breakdown of the internal components of the Ethernet switch 102 and/or end device 120. It is also apparent that such damage could occur at a critical time, thereby damaging the overall network precisely when communication is most critical.
Other major requirements for electronic devices used in substations as part of a protection and control system is reliable operation during periods of high electromagnetic interference (EMI). Substation environments can have multiple phenomena, which generate high levels of EMI (as shown for instance in Table 1 below).
TABLE 1Table 1: EMI Phenomena in the Substation - Sourcesand Causes, Corresponding IEC and IEEE Type TestsCorrespondingCorrespondingElectromagneticIEEE 1613IEC 61850-3PhenomenaSources and CausesType TestType TestAC voltage dips, shortFaults and switchingIEC 61000-4-11interruptions and voltagein the power supplyvariationsnetworkDC voltage dips, shortPower supply faultIEC 61000-4-29interruptionsand switching, lackof battery chargingRipple on d.c. powerAC rectification,IEC 61000-4-17supplybattery chargingConducted disturbances inInduction fromIEC 61000-4-16the rangeindustriald.c. to 150 kHzelectronics, filters(including the powerleakage current, faultfrequency)current at the powerfrequency, etc.Surge 100/1 300 □sBlowing of fusesIEC 61000-4-5Surge 1.2/50 □s-8/20 □sFault in powerIEC 61000-4-5network, lightningSurge 10/700 □sEffect of lightningIEC 61000-4-5ontelecommunicationlinesOscillatory waves: ringSwitchingIEC 61000-4-12wavephenomena, indirecteffect of lightningFast transient/burstSwitching of reactive loads,IEEE C37.90.1IEC 61000-4-4relay contact bouncing,switching in SF6Oscillatory waves:HV switching byIEEE C37.90.1IEC 61000-4-12damped oscillatory waveisolatorsConducted disturbances,Radiation by radio-IEC 61000-4-6induced byfrequency emittersradio-frequency fieldsElectrostatic dischargeDischarge of staticIEEE C37.90.3IEC 61000-4-2electricity byoperator, furniture,etc.Power frequency magneticCurrent in powerIEC 61000-4-8fieldcircuits, earthcircuits and networkPulse magnetic fieldLightning current inIEC 61000-4-8earth conductors andnetworkDamped oscillatoryMV and HVIEC 61000-4-8magnetic fieldswitching byisolatorsRadiated, radio-frequencyRadiation by radio-IEEE C37.90.2IEC 61000-4-3electromagnetic fieldfrequency emitters
Since the substation local area network LAN is becoming an integral part of the protection and control system it would therefore be desirable for the Ethernet switch, which may form the backbone of the substation LAN, to be as reliable and robust as the IEDs (Intelligent Electronic Devices) which have been specifically designed to operate reliability in harsh substation environments and which connect to the Ethernet switch (i.e. the substation LAN). One such class of devices are known as protective relaying IEDs. As such, it would be desirable for the switch to have the same level of immunity to EMI as the protective relaying IEDs. In more recent years, both the EEC and IEEE (Institute of Electrical and Electronics Engineers) have issued international standards (IEC 61850-3 2002, IEEE 1613 2003 dated Aug. 12, 2003) to specifically address the EMI immunity requirements of communications networks and systems in substations.